The present invention relates to a ratchet mechanism for a hand tool and, in particular, to a ratchet mechanism for locking the jaws of a hand tool such, as for example, a surgical forceps, in a desirable position.
Pliers-shaped tools generally have jaws positioned by movable plural handles. A typical pliers-shaped tool has two lever arms that intersect at a pivot point so that the two ends of the arms form first and second handles that an operator can separate or close. For certain uses, it is desirable for the operator to be able to lock the handles of a pliers-shaped tool in a desired position, which may be open, closed, or somewhere between those two extremes. For example, it is desirable during a surgical procedure for an instrument to clamp an object with the jaws remaining in position without the user having to apply a force to the handles. Various known locking mechanisms are used to lock the handles of pliers-shaped tools.
Pliers-shaped surgical instruments such as forceps use a locking mechanism to obtain a graduated closing of the forceps. In this manner, the jaws of the device may be locked in a closed, open or in between position, and a graduated closing of the forceps may be obtained. One type of locking mechanism used with forceps is a ratchet mechanism comprising a toothed member, one end of which is connected to one end of a first forceps handle. A longitudinal edge of the bar has a set of angled teeth that are engageable with the end of the second forceps handle. The end of the toothed member, that is remote from the hinge is unattached, but the bar is urged toward the forceps handles by a spring, causing contact between the teeth and the second forceps handle. To lock the forceps jaws in a closed position, the operator must squeeze the handles until the end of the second forceps handle engages the teeth of the toothed bar at the desired position. To unlock the forceps, the handles of the forceps are squeezed together slightly to release the engagement between the second forceps handle and the teeth, and the ratchet bar is lifted off the teeth with manual pressure. This locking mechanism suffers from the disadvantage that the unattached second end of the toothed member is not contained by the second handle such that it can move out of position so that it does not engage and lock with the second handle. The unattached and unconstrained second end often requires the operator to use two hands to operate the instrument. The locking mechanism further suffers from the disadvantage that the angled teeth can cut and nick the operator""s hand, a particular disadvantage during a surgical procedure where the gloves of the surgeon could be torn and the surgeon""s hands cut.
Another pliers-shaped tool having a locking mechanism is disclosed in U.S. Pat. No. 5,297,538, which describes a surgical retractor/compressor two removable, serrated locking mechanisms that are used to lock the arms of the pliers-shaped device in either a retraction or a compression mode. In this type of device, one locking mechanism at a time is removably attached to the surgical instrument. One locking mechanism has serrations that are angled in one direction. The other locking mechanism has serrations that are angled in the opposite direction. When a locking mechanism is attached to the surgical instrument, one end of the locking mechanism clips onto one handle, and the serrations in the locking mechanism engage with one of two oppositely angled sets of serrations that are formed on the second handle of the instrument, thereby locking the handles in either a retraction or a compression mode. Releasing or unlocking the handles typically requires the user to use both hands to hold the instrument handles and pull the locking mechanism to release it from the serrations. To do so, the user must apply a force transverse to that which is normally exerted when gripping a pliers-shaped tool. This instrument also suffers the drawback of having angled teeth and serrations which can scratch, cut and nick an operator""s hands or gloves.
Yet another locking mechanism for a pliers-shaped tool is disclosed in U.S. Pat. No. 4,896,661, which describes a multi-purpose orthopedic ratcheting forceps having interchangeable tip elements and a reversible ratchet mechanism for controlling the tip elements or jaw portions. The ratchet mechanism of that invention has a multi-position pawl mechanism on a first arm of the tool. A curved ratchet toothed member is secured in a channel of the second tool arm. The toothed member extends toward the first arm and passes through the pawl mechanism, where a movable pawl is engageable with the toothed member. The operator must move the pawl mechanism to engage and disengage the teeth of the ratchet from the pawl. When the pawl is moved to a first position, the arms of the forceps device pivot to ratchet open the jaw portions. When the pawl is moved to a second position, it allows the arms to ratchet closed the jaws. In the third position, the pawl is disengaged from the ratchet toothed member. Thus, the operator must re-position the pawl mechanism to cause both engagement and disengagement of the pawl. Furthermore, the sharp teeth of the curved ratchet member are in close proximity with, and point toward, the hand grip of the forceps device, thus posing a risk of catching or nicking the operator""s glove or hand.
It is desirable to provide a locking mechanism for a pliers-shaped tool whereby a controlled closing or opening of the tool jaws can be achieved with a mechanism that minimizes the risk of catching or nicking the hands or gloves of an operator, and wherein the tool handles and jaws can be adjusted or repositioned in a simple, easy to use manner with one hand. It is also desirable to provide a locking mechanism that limits the opening of the tool handles and facilitates one-handed use for all applications of the tool.
It is an object of one or more embodiments of the present invention to provide a locking mechanism for a pliers-shaped tool whereby a controlled closing or opening of the tool jaws can be achieved with a mechanism that minimizes the risk of catching or nicking the hands or gloves of an operator, and wherein the tool handles and jaws can be adjusted or repositioned in a simple, easy to use manner with one hand. It is a further object of one or more embodiments to provide a locking mechanism that limits the opening of the tool handles and facilitates one-handed use for all applications of the tool.
In one embodiment, the present invention is directed to a hand tool that has first and second handle portions, the second handle portion having a pawl associated therewith, and a ratchet bar having first and second terminal ends. The toothed bar or ratchet bar has a plurality of teeth, each one of which has a free end. The toothed bar may further include at least one shield member adjacent the teeth and having at least a portion extending beyond the free ends of the teeth. The toothed bar is preferably pivotally attached at its first terminal end to the first handle portion and the teeth of the toothed bar engage the pawl associated with the second handle portion. The first handle portion of the hand tool may include a biasing spring adapted and configured to pivot the toothed bar into engagement with the pawl. The biasing spring may comprise a leaf spring mounted to the first handle portion. The second handle portion may have an opening through which the toothed bar slides. The toothed bar may have a catch to prevent it from becoming disassociated from the second handle, by for example, sliding out of the opening. The second handle portion may also have a stop to prevent the toothed bar from pivoting away from the pawl.
In a further embodiment, the invention is directed to a ratchet mechanism for preventing undesired relative movement of two handle portions of a hand tool, including a toothed bar that has a first end which may be adapted and configured to be pivotally connected to at least one handle portion and a second end which may be adapted and configured to move relative to the other handle portion when the handle portions undergo relative movement. The toothed bar has a plurality of teeth designed and configured to interact with a pawl on the hand tool, the teeth further having free ends, and the toothed bar may include at least one shield member having at least a portion which extends beyond the free ends of the teeth. An opening may be formed in the other handle, and the toothed bar slides through the opening. The first end of the toothed bar may be designed and configured to receive a biasing force to pivot the toothed bar into engagement with the pawl. Furthermore, the first end of the toothed bar may be designed and configured to interact with a free end of a leaf spring mounted to the handle portion of the hand tool.
The hand tool and/or the ratchet mechanism may have a catch on the toothed bar to prevent the toothed bar from sliding completely through the opening. In one embodiment, two shield members are located adjacent the teeth of the toothed bar. Alternately, the toothed bar has two rows of teeth and at least one shield member located between the two rows of teeth. When the toothed bar has two rows of teeth the pawl may have a slot. The two rows of teeth may have two exposed lateral edges that are rounded and/or tapered toward the shield member.
The toothed bar may be manufactured in any number of ways including for example machining and/or casting, and may be made from any number of materials. The toothed bar further may be designed and configured to prevent the handle portions of the tool from separating unless an operator disengages the teeth from the pawl. The teeth may be arranged as sawtooth serrations.
In a further embodiment, the invention is a hand held tool having a first extending member; a second extending member having an opening associated therewith and a pawl. The hand held tool also has a working end movable by relative movement of the extending members, and a toothed bar having a first end pivotally connected to the first extending member and a second end adapted and configured to move through the opening in the second extending member. The toothed bar has teeth to engage the pawl to prevent undesirable relative movement of the first and second extending members.
Furthermore, the first and second extending members may be moved relative to each other in both directions by use of one hand of the operator. The toothed bar of the hand held tool may have a longitudinal axis between the first end and the second end, and the teeth and pawl may be configured to have contact surfaces that are substantially perpendicular to the longitudinal axis of the toothed bar. The toothed bar may also be curved.
The first and second extending members of the hand held tool may be designed and configured to prevent the toothed bar from being disassociated from the second extending member. In one embodiment, a stop may further prevent the toothed bar from pivoting away from the second extending member.
Furthermore, the hand held tool may be provided with a catch on the toothed bar to prevent the toothed bar from sliding through the opening. The opening may have a U-shape having an open back.
The hand held tool may also have a biasing member to urge the teeth into engagement with the pawl. The biasing member that urges the teeth into engagement with the pawl may be a leaf spring associated with the first extending member. The leaf spring biases the toothed bar to rotate about a pivotal connection on the hand held tool. The biasing member may alternatively engage the toothed bar and the second extending member.
The hand tool may be a surgical instrument, and the ratchet mechanism may be designed and adapted for use with a surgical instrument.